change API contract: disallow zero-sized images or surfaces

src/image/SkSurface.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkSurface_Base.h"
 #include "SkImagePriv.h"
 #include "SkCanvas.h"
@@ skipping 105 matching lines @@
 
 static SkSurface_Base* asSB(SkSurface* surface) {
     return static_cast<SkSurface_Base*>(surface);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SkSurface::SkSurface(int width, int height, const SkSurfaceProps* props)
     : fProps(SkSurfacePropsCopyOrDefault(props)), fWidth(width), fHeight(height)
 {
-    SkASSERT(fWidth >= 0);
-    SkASSERT(fHeight >= 0);
+    SkASSERT(fWidth > 0);
+    SkASSERT(fHeight > 0);
     fGenerationID = 0;
 }
 
 SkSurface::SkSurface(const SkImageInfo& info, const SkSurfaceProps* props)
     : fProps(SkSurfacePropsCopyOrDefault(props)), fWidth(info.width()), fHeight(info.height())
 {
-    SkASSERT(fWidth >= 0);
-    SkASSERT(fHeight >= 0);
+    SkASSERT(fWidth > 0);
+    SkASSERT(fHeight > 0);
     fGenerationID = 0;
 }
 
 uint32_t SkSurface::generationID() {
     if (0 == fGenerationID) {
         fGenerationID = asSB(this)->newGenerationID();
     }
     return fGenerationID;
 }
 
@@ skipping 40 matching lines @@
 SkSurface* SkSurface::NewRenderTarget(GrContext*, const SkImageInfo&, int, const SkSurfaceProps*) {
     return NULL;
 }
 
 SkSurface* SkSurface::NewScratchRenderTarget(GrContext*, const SkImageInfo&, int sampleCount,
                                              const SkSurfaceProps*) {
     return NULL;
 }
 
 #endif